Yeah, being the daughter of a Nazi would make any woman go crazy. Introduced in Captain America #290 (1983) by J.M. DeMatteis and Ron Frenz, when the Red Skull wanted an heir to carry on his legacy, he raped a washerwoman and impregnated her. The woman died at childbirth and Red Skull was going to kill the baby because she was a girl but Susan Scarbo, Mother Night, convinced him to let her live. Skull left the baby, named Sinthea, to be raised and indoctrinated in the Skull’s view by Scarbo. Skull would eventually return to her as a child and accelerated her growth with a machine. He also gave her powers.

As Mother Superior, she became the leader of the Sisters of Sin, a group of female orphans who also had their age accelerated and given powers. They were sent to attack Captain America, until they were de-aged during a fight with Cap. When Scarbo, now Mother Night, became the leader, Synthea became Sister Sin. Following the capture of the capture, Synthea was taken in by SHIELD, who tried to re-educate her into being a normal girl. However, following the assassination of Red Skull, Crossbones broke into the prison and kidnapped her. He spent weeks torturing her until the SHIELD conditioning broke. She entered into a relationship with Crossbone and took on the name of Sin. She was later reunited with her father when he inhabited the body of Alexander Lukin.

As part of the Skull’s master plan, she disguised herself as a nurse as Crossbones shot a bullet at Captain America when he was arrested following the Civil War. She kidnapped Sharon Carter and revealed to her that Sharon was really the person who killed Cap. The two would fight brutally, resulting in Sharon losing the baby of Steve’s she was carrying. After Skull tried to take over Cap’s revived body, she was caught in an explosion, horribly scaring her face to have a similar appearance to her father. She was sent to an insane asylum where she was approached by Zemo, who wanted to know how to kill Bucky. She was later freed by Master Man and made the leader of Hydra as the new Red Skull.

She would later kidnap Bucky, who was now Captain America, and Black Widow and put them on trial but they escaped. She would later team up with Zemo to find the Book of The Skull which told them of an enchanted hammer. They found the hammer and she betrayed Zemo, taking the hammer for herself. However, what she didn’t realize was that the hammer would turn her into Skadi, signaling the return of the Serpent and the start of Fear Itself. After the defeat of the Serpent, her hammer was taken from her by Odin. She later teamed up with the new High Council of Hydra to defame Sam Wilson who had become Captain America following Steve being aged into an old man.

After her father returned in a cloned body, she would become his lieutenant. During one of the meetings to reform Hydra, Kubik appeared, looking for the Skull. She used the Cosmic Cube’s power to heal Sin’s face. She would continue to work for her father until he was killed by the Hydra Captain America. She would later slaughter a group of archaeologists in her search for the mask of Erida, a goddess of hate. She used this power to make some local go into a frenzy, which she feed on. The newly formed Avengers Emergency Response Squad defeated her, with Photon (Rambeau) using Cap’s shield to destroy the mask. She would disintegrated seemingly dying.